When a piercing operation is performed by means of wire cut electric discharge machining, a core to be cut off from a workpiece body is held by the use of a jig such as a magnet or suction device, so that the core will not be dropped out from the workpiece body. However, if the core is small in size, the core may be dropped out from the workpiece body and may damage a wire (tool electrode) or parts of an electric discharge machine. Therefore, in the prior art, so-called coreless-machining is carried out, in which electric discharge machining is effected over the whole of a core area while moving the wire in the core area, so as to cause the entire core to be melted and thus prevented from being dropped out.
In the case of using a programming unit for electric discharge machining to create coreless-machining data (program), a pocket machining data creating function of a programming device for milling is conventionally utilized since the prior art device has no function used exclusively for the coreless-machining data creation. In this case, however, a definition inputting operation for defining the procedure of the coreless-machining is complicated, and the created NC data may conflict with inhibited matters inherent to the wire cut electric discharge machining. For example, unlike the milling, in the wire cut electric discharge machining for machining a workpiece by the use of a wire which extends through the workpiece, it is inhibited to cause a wire to be retarded from the workpiece, and then rapidly moved to and positioned at the machining starting position on the workpiece. When an inhibited operation of this kind is erroneously defined in the programming operation, wire disconnection may occur.